A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power an aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The fan section is positioned at the front of the engine, and includes a fan that induces air from the surrounding environment into the engine and accelerates a fraction of this air toward the compressor section. The remaining fraction of induced air is accelerated into and through a bypass plenum, and out the exhaust section.
The compressor section is configured to raise the pressure of the air to a relatively high level. In particular, the compressor section includes an impeller that has a plurality of vanes extending therefrom that accelerate and compress the air. The compressed air then exits the compressor section, and is energized by the combustor section and flowed into the turbine section to cause rotationally mounted turbine vanes to rotate and generate energy.
Over time, certain components of the engine may become worn and may need to be replaced or repaired. For example, impeller vanes may become deformed or damaged due to prolonged exposure to high temperature air and continuous bombardment by particles during engine operation. Impeller vane repairs often employ welding processes, such as, for example, laser welding, tungsten inert gas welding, or plasma arc welding, where a power source is used to melt a filler material, and a sufficient amount of the melted material is deposited onto a desired area of the impeller. After the material cools and hardens, the area is machined into a desired configuration.
When the filler material is in a molten state, it is preferably isolated from contact with oxygen. Oxygen may oxidize or contaminate the filler material and cause it to become relatively brittle or weak. To prevent such contamination, the impeller is typically bathed in a noble gas, such as argon. The gas, which is typically heavier than air, is generally supplied through a weld head, spread through a metal screen either coupled or adjacent thereto, and poured directly onto the impeller.
Although the above-mentioned technique for bathing the impeller is adequate, it suffers from certain drawbacks. Specifically, because the impeller vanes and shaft do not form enclosed cavities, the gas continuously spills off of the impeller and thus, needs to be continually supplied. As a result, a large amount of gas is used. Additionally, the gas may not sufficiently bathe certain portions of the impeller, and, consequently, the impeller may not be entirely covered in the gas. Thus, the likelihood of the filler material becoming oxidized increases.
Hence, there is a need for a mask that reduces the amount of gas used in a welding process. Additionally, it is desirable that the mask allow a repair area of the impeller to be entirely covered by the gas to reduce the likelihood that the filler material will become oxidized.